1. Field of the Invention
This invention relates to flexible composites and to articles fabricated from same having enhanced flexibility. A more preferred aspect of this invention relates to flexible composites and articles having improved protection against penetration by such threats as bullets, knives, ice picks, flechettes and the like.
2. Prior Art
Since the beginning of recorded history, a combination of rigid plates or panels affixed to a flexible backing, usually fabric or leather, has been used extensively as body armor in diverse areas of the world. (Charles Ffoulkes, Armour and Weapons Oxford at the Clarendar Press, 1909; H. Russell Robinson, Armour, London: Herbert Jenkins, 1967; A. M. Snodgrass, Arms and Armour of the Greeks, Cornell University Press, Ithaca, N.Y., 1967; Vesey Norman, Arms and Armor, G. P. Putnam's Sons, New York and Claude Blair, European Armous. The McMillan Company, New York, 1959. During the 14th century a cloth or leather garment lined with metal plates, known as a coat of plates, was the most widely used type of body defence. It appears that the plates were rectangular in shape and their arrangement prevented draping of the armor or flexing on the bias. Almost certainly, this armor limited the mobility of the wearer. A development from the coat of plates was the brigandine which remained in general use until the 17th century. In the 15th century and later the brigandine consisted of a coat of plates made of small lames which could work over each other, thus producing flexible protection. A variant of the brigandine, the jack, (15th century) consisted of many small plates of iron or horn secured between layers of canvas by a trellis-work of stitches. A variant of the jack was the "pennyplate coat" and was constructed from small overlapping iron discs with each disc riveted to a canvas backing. (See Claude Blair, European Armour, The MacMillan Company, New York 1959)
Roy C. Laible, Ballistic Materials and Penetration Mechanics, Elsevier Scientific Publishing Co. Amsterdam Oxford-New York, 1980 describes an infantry vest utilizing 149 titanium plates attached to four layers of nylon ballistic fabric backing. The plates overlapped and incorporated three slits to allow them to slide, thus providing flexibility. The plates were rectangular or square in shape and appear to be curved in one plane.
U.S. Pat. No. 4,316,286 describes a bullet-proof plate assemblies, utilizing hinged plates, but such assemblies utilize relatively large roughly rectangular shaped panels. Such an approach is unlikely to lead to flexibility required for an infantry vest.
U.S. Pat. No. 4,559,251 describes a material for protective clothing which has been developed based on an assembly of hexagonal rigid plates. Although such a construction is an improvement over a single rigid panel it appears that the structure will have inherent limitations in flexibility, contrary to claims in the patent, which would limit its usefulness as infantry body armor.
U.S. Pat. No. 4,483,020 describes a ballistic vest which incorporates essentially square plates which interlock when flexed inward. It is claimed that such an arrangement reduces blunt trauma. A similar vest is disclosed in U.S. Pat. No. 4,660,223 which incorporates multiple titanium panels with each titanium panel to each other except by overlying and underlying felted material. In this disclosure, all panels appear to be based on square or rectangular considerations.
A design for body armor has been disclosed in U.S. Pat. No. 4,535,478 in which modular panels have been incorporated into a carrier garment. No unusual geometric considerations were disclosed.
Multiple plate body armor has been disclosed in U.S. Pat. No. 4,680,812 which allows flexibility but protects the body from hyper-extension, thus protecting against spinal injury.
Flexible body armor has been disclosed in U.S. Pat. No. 3,894,472 which has a central support sheet with the plates arranged in a checkerboard pattern. The pattern of the plates on one face are the reverse of the pattern on the opposite face. This approach claims complete coverage by rigid plates, coupled with appropriate flexibility.
An infantry body armor system has been disclosed in U.S. Pat. No. 3,557,384 which is claimed to provide protection against both fragments and small arms fire. This system uses a single plate on the front of the torso and a single plate on the back of the torso to provide protection against small arms fire. Relatively large plates may be utilized on a limited and specific portions of the torso.
A complex body armor system has been disclosed in U.S Pat. No. 3,577,836 which incorporates multiple Telflon discs which are circular when viewed from the front but are elliptical in cross-section. It is claimed that the low coefficient of friction facilitates the deflection of projectiles and the elliptical cross-section minimizes the number of projectiles which can impact normal to the disc surface.
Ballistic articles such as bulletproof vests, helmets, structural members of helicopters and other military equipment, vehicle panels, briefcases, raincoats and umbrellas containing high strength fibers are known. Fibers conventionally used include aramid fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon fibers, ceramic fibers, glass fibers and the like. For many applications, such as vests or parts of vests, the fibers are used in a woven or knitted fabric. For many of the applications, the fibers are encapsulated or embedded in a matrix material.
U.S. Pat. Nos. 4,623,574 and 4,748,064 disclose a simple composite structure comprising high strength fibers embedded in an elastomeric matrix. The simple composite structure exhibits outstanding ballistic protection as compared to simple composites utilizing rigid matrices, the results of which are disclosed in the patents. Particularly effective are simple composites employing ultra-high molecular weight polyethylene and polypropylene such as disclosed in U.S. Pat. No. 4,413,110.
U.S. Pat. Nos. 4,737,402 and 4,613,535 disclose complex rigid composite articles having improved impact resistance which comprise a network of high strength fibers such as the ultra-high molecular weight polyethylene and polypropylene disclosed in U.S. Pat. No. 4,413,110 embedded in an elastomeric matrix material and at least one additional rigid layer on a major surface of the fibers in the matrix. It is disclosed that the composites have improved resistance to environmental hazards, improved impact resistance and are unexpectedly effective as ballistic resistant articles such as armor.
U.S. Pat. No. 4,650,710 discloses a flexible article of manufacture comprising a plurality of first flexible layers arranged in a first portion of the article, each of said first layers consisting essentially of fibers having a tensile modulus of at least about 300 g/denier and a tenacity of at least about 15 g/denier and a tenacity of at least about 15 g/denier and a plurality of a second flexible layers arranged in a second portion of said article, each of said second flexible layers comprising fibers, the resistance to displacement of fibers in each of said second flexible layers being greater than the resistance to displacement in each of said first flexible layers.
Other ballistic resistant articles are described in U.S. Pat. Nos. 4,916,000; 4,403,012, 4,457,985; 4,737,401; 4,543,286; 4,563,392 and 4,501,856.